Significance of the injection timing of ephedrine to reduce the onset time of rocuronium

We postulated that the onset time of rocuronium can be accelerated effectively if it is administered at the time when the effect of ephedrine on cardiac output has reached its maximum. Seventy-five male, anaesthetised, patients were randomly allocated to three groups. Ephedrine 70 μg.kg⁻¹ was administered at 4 min (Early) or 30 s (Late) before administering rocuronium. The control group received saline at 4 min and at 30 s before rocuronium. The onset time of rocuronium in the Early group was significantly shorter than in the Control group, but there was no difference in the onset time between the Late and Control groups. There were no significant differences in the intubating conditions of the three groups. Ephedrine 70 μg.kg⁻¹ can reduce the onset time of rocuronium effectively if rocuronium is administered at 4 min following the ephedrine injection, when the effect of ephedrine on cardiac output is expected to reach its maximum.